Low profile, high stretch knit prosthetic device

ABSTRACT

A radially expandable stent-graft endoprosthesis is provided. The graft included in the stent-graft is a knitted tubular structure circumferentially disposed and securably attached to the stent. The knitted tubular structure has a knit pattern of interlacing yarns in an Atlas or a modified-Atlas pattern to provide greater than 150 percent longitudinal stretchability. A knitted tubular graft and a knitted medical fabric with greater than 150 percent longitudinal stretchability are also provided.

FIELD OF INVENTION

[0001] The present invention relates generally to a tubular implantableprosthesis having a knitted textile structure. More particularly, thepresent invention relates to an endoprosthesis with a knitted textilestructure having increased longitudinal stretchability.

BACKGROUND OF RELATED TECHNOLOGY

[0002] An intraluminal prosthesis is a medical device used in thetreatment of diseased blood vessels. An intraluminal prosthesis istypically used to repair, replace, or otherwise correct a diseased ordamaged blood vessel. An artery or vein may be diseased in a variety ofdifferent ways. The prosthesis may therefore be used to prevent or treata wide variety of defects such as stenosis of the vessel, thrombosis,occlusion or an aneurysm.

[0003] One type of intraluminal prosthesis used in the repair ofdiseases in various body vessels is a stent. A stent is a generallylongitudinal tubular device formed of biocompatible material which isuseful to open and support various lumens in the body. For example,stents may be used in the vascular system, urogenital tract and bileduct, as well as in a variety of other applications in the body.Endovascular stents have become widely used for the treatment ofstenosis, strictures and aneurysms in various blood vessels. Thesedevices are implanted within the vessel to open and/or reinforcecollapsing or partially occluded sections of the vessel.

[0004] Stents generally include an open flexible configuration. Thisconfiguration allows the stent to be inserted through curved vessels.Furthermore, this configuration allows the stent to be configured in aradially compressed state for intraluminal catheter implantation. Onceproperly positioned adjacent the damaged vessel, the stent is radiallyexpanded so as to support and reinforce the vessel. Radial expansion ofthe stent may be accomplished by inflation of a balloon attached to thecatheter or the stent may be of the self-expanding variety which willradially expand once deployed. Structures which have been used asintraluminal vascular grafts have included coiled stainless steelsprings; helically wound coil springs manufactured from a heat-sensitivematerial; and expanding stainless steel stents formed of stainless steelwire in a zig-zag pattern. Examples of various stent configurations areshown in U.S. Pat. No. 4,503,569 to Dotter; U.S. Pat. No. 4,733,665 toPalmaz; U.S. Pat. No. 4,856,561 to Hillstead; U.S. Pat. No. 4,580,568 toGianturco; U.S. Pat. No. 4,732,152 to Wallsten and U.S. Pat. No.4,886,062 to Wiktor, all of whose contents are incorporated herein byreference.

[0005] A graft is another commonly known type of intraluminal prosthesiswhich is used to repair and replace various body vessels. A graftprovides a lumen through which blood may flow. Moreover, a graft isoften configured to have porosity to permit the ingrowth of cells forstabilization of an implanted graft while also being generallyimpermeable to blood to inhibit substantial leakage of bloodtherethrough. Grafts are typically tubular devices which may be formedof a variety of materials, including textile and non-textile materials.

[0006] A stent and a graft may combined into a stent-graftendoprosthesis to combine the features thereof. The graft, however, inthe stent-graft endoprosthesis should comply with the implantationrequirements of the stent which often include collapsing the stent forplacement at an implantation site and expansion of the stent forsecurement thereat. Grafts which cannot easily accommodate thelongitudinal and/or radial dimensional changes from a unexpanded orcollapsed state to an expanded stent often complicate the implantationof the stent-graft. For instance, some grafts are folded in thecollapsed or unexpanded state and must be subsequently be unfolded toaccommodate the expanded stent. The unfolding of the graft, however,often complicates the placement of the graft on the stent and theimplantation of the stent-graft itself. Alternatively, noncontiguousgrafts have been used with expandable stent-grafts. Upon expansion ofthe stent, however, portions of the noncontiguous graft often separateto accommodate the stent expansion. This separation leaves gaps in thegraft structure thereby permitting the leakage of blood through thesegaps.

[0007] Thus, there is a need for a graft that compliments theimplantation of an expandable stent of a stent-graft endoprosthesis. Inparticular, there is need for a graft that is securably attached to thestent in both the expanded and unexpanded state without complicating themechanical dynamics of the stent or the graft.

SUMMARY OF THE INVENTION

[0008] The present invention provides an implantable tubular prosthesishaving a radially expandable tubular stent structure having a firstdiameter and capable of longitudinal expansion or contraction to achievea second diameter which is different from the first diameter and atubular knitted tubular graft circumferentially disposed and securablyattached to the stent. The graft has a pattern of interlaced wale andcourse yarns in a knit pattern to permit longitudinal expansion orcontraction of the graft substantially consistent with the longitudinalexpansion or contraction of the stent.

[0009] The prosthesis of the present invention is capable oflongitudinal expansion from 50 to 200 percent by length from a quiescentstate. Alternatively, the prosthesis of the present invention is capableof 50 to 200 percent longitudinal contraction by length to achieve asubstantially quiescent state from an unexpanded state. Furthermore, thetextile graft of the present invention is substantially fluid-tight inits quiescent state.

[0010] To achieve such a degree of longitudinal expansion or contractionthe textile graft includes a stretchable knit pattern. The pattern is awarp knitted pattern having a set yarns diagonally shifted over one ormore yarns to form a loop between engaging yarns. Furthermore, theengaging yarns alternately form open loops where the engaging yarns donot cross over themselves and closed loops where the engaging yarnscross over themselves. The knit pattern is generally described as aAtlas or an modified-Atlas knit pattern. Such patterns depart a highdegree of flexibility and stretchability to the textile graft of thepresent invention.

[0011] The knit pattern further includes a plurality of front and backyarns formed from single stitches, where the single stitches are deposedin a plurality of stitch repeating patterns. A first stitch has arepeating pattern traversing diagonally by two or more needle positionsand a second stitch has a repeating pattern alternatively traversingdiagonally by three or more needle positions and by one needle position.

[0012] In one aspect of the present invention an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state in provided. The prosthesis includes a radiallycontractible and longitudinally expandable tubular stent having aquiescent diameter and quiescent length capable of longitudinalexpansion to the elongated state having an elongated length and acontracted diameter, wherein the elongated length is greater than thequiescent length and the contracted diameter is smaller than thequiescent diameter, and further wherein the stent is capable ofresiliently returning from the elongated state to the quiescent state.The prosthesis further includes a tubular knitted tubular graftcircumferentially disposed and securably attached to the stent in thequiescent state. The graft has a pattern of yarns interlaced intostitches in a knit pattern capable of resilient longitudinal elongationand resilient radial contraction of the graft to the elongated state.Furthermore the graft has from 400 to 900 stitches per square centimeterto provide compliancy in the quiescent state.

[0013] In another aspect of the present invention an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent as described above and a tubular knittedtubular graft having a warp knitted pattern of yarns forming a textilelayer having an interior surface and an exterior surface, whereininterior yarns predominate the interior surface and form loops in thelongitudinal direction of the prosthesis, and exterior yarns predominatethe exterior surface and are diagonally shifted over one or more of theinterior yarns in an alternating pattern along a width of the prosthesisto engage the interior yarns. The interior yarn alternately interlacesthe engaging exterior yarn to form open loops where the interior yarndoes not cross over itself and closed loops where the interior yarn doescross over itself.

[0014] In another aspect of the present invention an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent and a tubular knitted tubular graftcircumferentially disposed and securably attached to the stent in thequiescent state, where the graft has greater than about 350 stitches persquare centimeter in its knit pattern to provide compliancy of the graftand wherein the prosthesis is capable of longitudinal expansion from 50to 200 percent by length.

[0015] In yet another aspect of the present invention, an implantabletubular prosthesis capable of longitudinal expansion from a quiescentstate to an elongated state includes a radially contractible andlongitudinally expandable tubular stent and tubular knitted tubulargraft circumferentially disposed and securably attached to the stent.The graft has a knit pattern with greater than about 350 stitches persquare centimeter while also having a wall thickness from about 0.3 toabout 0.4 millimeters.

[0016] In still another aspect of the present invention, an implantabletubular prosthesis capable of longitudinal expansion from a quiescentstate to an elongated state includes a radially contractible andlongitudinally expandable tubular stent and tubular knitted tubulargraft circumferentially disposed and securably attached to the stent,wherein the stent and the graft are resiliently deformable between thequiescent and elongated states and further wherein the graftnon-bulgingly contracts from the elongated state to the quiescent stateto circumferentially abut the stent.

[0017] In still yet another aspect of the present invention, animplantable tubular prosthesis capable of radial expansion from aquiescent state to a radially expanded state includes a radiallyexpandable and longitudinally contractible tubular stent and a tubularknitted tubular graft circumferentially disposed and securably attachedto the stent in the quiescent state. The graft has a pattern of yarnsinterlaced into stitches in a knit pattern capable of resilient radialexpansion and resilient longitudinal contraction of the graft to theelongated state and has from 400 to 900 stitches per square centimeterto provide compliancy for the graft in the quiescent state.

[0018] In other aspects of the present invention, a non-textile,desirably ePTFE, layer is provided with the endoprosthesis of thepresent invention. Moreover, a textile graft capable of resilientelongation and having from 400 to 900 stitches per square centimeter isprovided. Furthermore, an implantable medical fabric is provided. Themedical fabric is a knitted textile with a high degree of stretchabilitybecause of the Atlas and the modified-Atlas stitches used to form thefabric. A method for producing the high stretch knit prosthetic deviceis also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a partial cut-away perspective view of an endoprosthesisof the present invention having a stent and a graft both capable oflongitudinal expansion or contraction.

[0020]FIG. 2 is a cross-sectional view of the stent-graft of FIG. 1taken along the 2-2 axis.

[0021]FIG. 3 depicts the stent-graft of FIG. 2 having a longitudinallyexpanded length.

[0022]FIG. 4 depicts a wire stent in an expanded state according to thepresent invention.

[0023]FIG. 5 depicts the wire stent of FIG. 5 in an unexpanded state.

[0024]FIG. 6 depicts a slotted stent in a quiescent state according tothe present invention.

[0025]FIG. 7 depicts the slotted-stent of FIG. 6 in an expanded state.

[0026]FIG. 8 is a perspective view of a helical coil formed of a singlewound wire.

[0027]FIG. 9 is a perspective view of a stent having an elongatepre-helically coiled configuration.

[0028]FIG. 10 is a perspective view of the stent of FIG. 9 in a radiallyexpanded state.

[0029]FIG. 11 is a diagrammatic illustration of a textile portion of thegraft of FIG. 1 taken along the 11-11 axis.

[0030]FIGS. 12 and 13 depict yarn patterns for the textile portion ofFIG. 11.

[0031]FIG. 14 is a cross-sectional of the present invention whichfurther includes a layer of e-PTFE.

[0032]FIG. 15 is a partial perspective view of a knitted medical fabricof the present invention.

[0033]FIG. 16 is a photomicrograph showing a longitudinally expandedePTFE structure.

[0034]FIG. 17 is a photomicrograph of physically modified ePTFEstructure having enhanced elongation properties as compared to the ePTFEstructure of FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention addresses the problems associated withprior art stent-graph endoprosthesis. The stent-graft endoprosthesis ofthe present invention overcomes the disadvantages of presently availablestent-grafts by providing an expandable graft that complements anexpandable stent in both an expanded or contracted state. Furthermore,the graft of the present invention is knitted textile graft whichprovides greater stretchability than previously knitted or woven textilegrafts. Moreover, the knitted textile graft of the present invention hasa porosity to permit the ingrowth of cells for the stabilization ofimplanted endoprosthesis while also being generally impermeable toinhibit substantial leakage of blood therethrough.

[0036]FIG. 1 is a depiction of stent-graft 10 of the present invention.Stent-graft 10 is shown as a generally tubular structure with open ends16, 18 to permit the passage of a bodily fluid therethrough. Stent-graft10 includes textile graft 12 and stent 14. Textile graft 12 extendscircumferentially about stent 14. Textile graft 12 is securably attachedto stent 14. The attachment of textile graft 12 to stent 14 may beaccomplished by mechanically securing or bonding the textile graft 12and the stent 14 to one and the other. Mechanical securement includes,but is not limited to, the use of sutures, anchoring barbs, textilecuffs and the like. Bonding includes, but is not limited to, chemicalbonding, for instance adhesive bonding, thermal bonding and the like.

[0037] As depicted in FIG. 1, the textile graft 12 circumferentiallyextends about an outer stent surface 20. The present invention, however,is not so limited and other stent-graft configurations may suitably beused with the present invention. For instance, textile graft 12 may becircumferentially positioned along an inner surface of stent 14.Moreover, the longitudinal lengths of the stent 14 and the textile graft12 are not limited to substantially similar lengths as depicted inFIG. 1. For instance, textile graft 12 may be shorter than stent 14thereby leaving a portion of stent 14 without being covered by textilegraft 12.

[0038]FIG. 2 dimensionally depicts the stent-graft 10 of the presentinvention after securement within a bodily lumen (not shown) and FIG. 3dimensionally depicts the stent-graft 10′ prior to securement thereat.To navigate the stent-graft within a bodily lumen the nominal diameter,D₂, of stent-graft 10′ is smaller than the diameter, D₁, of stent-graft10. Correspondingly, the length, L₂, of stent-graft 10′ is larger thanthe length, L₁, of stent-graft 10. The textile graft 12 and the stent 14both conform to these general dimensional depictions for the navigationand securement of stent-graft 10 within a bodily lumen. The textilegraft 12 is elongated or stretched to accommodate the elongatedstent-graft 10′. Correspondingly, textile graft 12 is in a substantiallyquiescent state to accommodate the stent-graft 10 of FIG. 2.

[0039] Various stent types and stent constructions may be employed inthe invention. Useful stents include, without limitation, self-expandingstents and balloon expandable stents. The stents may be capable ofradially contracting or expanding, as well, and in this sense can bebest described as radially or circumferentially distensible ordeformable. Self-expanding stents include those that have a spring-likeaction which causes the stent to radially expand, or stents which expanddue to the memory properties of the stent material for a particularconfiguration at a certain temperature. Nitinol is one material whichhas the ability to perform well while both in spring-like mode, as wellas in a memory mode based on temperature. Other materials are of coursecontemplated, such as stainless steel, platinum, gold, titanium andother biocompatible metals, as well as polymeric stents.

[0040] The configuration of stent 14 may be of any suitable geometry. Asshown in FIG. 4, wire stent 22 is a hollow tubular structure formed fromwire strand 24 being arranged in what can be described as a “Z” or a“zig-zag” pattern. Wire strand 24 may be formed by, for example,braiding or spinning it over a mandrel. Alternatively, wire stent 24 maybe formed from more than one wire strand.

[0041] Wire stent 22 is capable of being radially compressed andlongitudinally extended, to yield wire stent 22′, as depicted in FIG. 5,for implantation into a bodily lumen. The degree of elongation dependsupon the structure and materials of the wire stent 22 and can be quitevaried. For example, the length of wire stent 22′ is from about 50% toabout 200% of the length of wire stent 22. The diameter of wire stent22′ may also be up to several times smaller than the diameter of wirestent 22.

[0042] In another aspect of the present invention, a slotted stent 26 isalso useful as part of the stent-graft 10. As depicted in FIG. 6,slotted stent 26 is suitably configured for implantation into a bodilylumen (not shown). Upon locating the slotted stent 26 at the desiredbodily site, slotted stent 26 is radially expanded and longitudinallycontracted for securement at the desired site. The expanded slottedstent 26′ is depicted in FIG. 7. Slotted stent 26′ is from about 50% toabout 200% greater in radial dimension as compared to slotted stent 26.

[0043] Other useful stents capable of radial expansion are depicted inFIGS. 8, 9 and 10. As depicted in FIG. 8, stent 28 is a helical coilwhich is capable of achieving a radially expanded state (not shown).Stent 29, as depicted FIG. 9, has an elongate pre-helically coiledconfiguration as shown by the waves of non-overlapping undulatingwindings. Stent 29 is capable of being radially expanded to expandedstent 29′ as depicted in FIG. 10. These helically coiled orpre-helically coiled stents are also useful with the practice of thepresent invention.

[0044] The textile graft 12 is a knitted textile graft. Knittinginvolves the interlooping or stitching of yarn into vertical columns(wales) and horizontal rows (courses) of loops to form the knittedfabric structure. Warp knitting is particularly useful with the textilegraft 12 of the present invention. In warp knitting, the loops areformed along the textile length, i.e., in the wale or warp direction ofthe textile. For a tubular textile, such as textile graft 12, stitchesextending in the axial or longitudinal direction of the tubular textileare called courses and stitches extending along the circumference of thetubular textile are called wales.

[0045] Conventional knitted tubular grafts often had to reduce or limitthe number of courses per unit length to obtain a flexible tubularstructure, i.e., a structure with longitudinal stretchability. Reducingthe number of courses per unit length, however, opens the macroporousstructure of the textile. A macroporous textile structure is notdesirable as a graft because such a structure is not a fluid tightstructure, i.e., blood will flow through the graft. Similarly, if thenumber of wales per unit length was too low, the graft would not sealblood flow. If the number of wales per unit length was too high, thegraft could dilate with time. Thus, conventional grafts were limited bythe total number of courses and wales per unit length, which is referredto as the number of picks per unit area or the pick size.

[0046] For example, textile tubular prostheses in a warp-knit or anAtlas-knit were typically limited to 4 to 16 courses per centimeter (10to 40 courses per inch) and to 4 to 16 wales per centimeter (10 to 40wales per inch) to provide a longitudinally stretchable tubularstructure. The pick size of these stretchable prostheses were limited toabout 16 to 62 stitches per square centimeter (100 to 400 stitches persquare inch). The textile graft 12 of the present invention is not solimited because of the novel knit pattern used to form the graft ascompared to more conventional knit patterns, such as tricot, locknit andthe like, or even previously used Atlas-knits.

[0047] Moreover, grafts are sometimes crimped with creases or foldswhich tend to reduce kinking when the graft is bent. The kinking alsoallows for some elongation of the graft, but such a crimped graft wouldnot be generally useful as a stent-graft because of the gaps that wouldresult between the stent and the crimped graft.

[0048] The textile graft 12 is configured to have a high degree ofstretchability. As used herein, the term stretchability and its variantsrefers to a textile capable of substantially reversible elongationbetween a quiescent state and a stretched state. Desirably thestretchability of the textile graft 12 is substantially compatible withthe dimensional changes associated with an expandable stent having botha expanded and an unexpanded or a contracted state as discussed above.Moreover, textile graft 12 is not a crimped graft and does non-bulginglycontract from the elongated state to the quiescent state. The textilegraft 12 substantially abuts the stent along both circumferential andlongitudinal portions of the stent without separating or bulging fromthe stent.

[0049] Knitting patterns useful in providing the desired stretchabilityinclude those knitting patterns that are not highly interlaced, such aspatterns that interlace each adjacent back and front yarn. An example ofa highly interlaced and commonly known knitted pattern is a Tricot orJersey pattern. In contrast the knitting pattern of the presentinvention is not highly interlaced to provide, among other things, thestretchability of the textile graft for use with an expandable stent.

[0050]FIG. 11 is an illustration of a portion 30 of the textile graft 12taken along the 11-11 axis. The knitted portion 30 is characterized as awarp knit atlas pattern. In FIG. 11, needle position in the coursedirection, i.e., vector 51, are noted by element numbers 32 a through 32h, and needle positions in the wale direction, i.e., vector 53, arenoted element numbers 34 a through 34 i. A yarn moves one needleposition in the course direction and one needle position in the waledirection before alternately interlacing with adjacent yarns. The needlepositions are indicated by dots 58. For example, yarn 36 c moves in thecourse direction from needle position 32 d to needle position 32 e, fromneedle position 32 e to needle position 32 d, from needle position 32 dto needle position 32 c, from needle position 32 c to needle position 32d, and then repeats this alternating pattern. As yarn 36 c moves in thecourse direction, it also moves generally in wale direction. Adjacentwales and adjacent courses are interlooped to form a warp knitted atlaspattern. The pattern is further described below in conjunction withFIGS. 12 and 13.

[0051] The knitted portion 30 is depicted as a single knitted layer inFIG. 11, however, the textile graft 12 of the present invention is notso limited. For instance, the knitted portion 30 may include more thanone layer of interconnected yarns. In such a multi-layered knittedtextile, yarns from one layer are often interlooped with yarns inanother layer to form the multi-layered knitted textile.

[0052] Textile graph 12 is flat knitted tubular structure to form such aflat-knitted tubular structure, two portions 30 are co-knitted to oneand the other and joined together by border yarns.

[0053]FIG. 12 depicts the yarn patterns of FIG. 11 by separating frontand back yarns from one and the other to more clearly illustrate theindividual yarn knit pattern and the repeating nature, if any, of theseindividual yarn knit patterns. As depicted in FIG. 12, front yarn 50 fis repeated about 10 times and then front yarn 54 f followed by frontyarn 54 f are knitted once. This ten-by-one-by-one pattern is repeatedto yield a technical front or exterior surface of the textile graft 12.The technical back of the textile graft 10 is depicted in FIG. 12 byrepeating back yarn 54 b four times followed by repeating back yarns 52b, 54 b and 52 b and further followed by repeating back yarns 50 b fourtimes. This back pattern is repeated to yield the technical back orinterior surface of the textile graft 12 of the present invention.

[0054] The knitting patterns for the front and back yarns are furtherillustrated in FIG. 13. The front and back yarns are interlaced in arelatively loose pattern. This pattern may be generally referred to asan Atlas pattern. A warp knit Atlas pattern is generally characterizedas a warp knit textile in which a set of yarns shifts diagonally one ormore wale per course for several courses, then returns to the originalposition. In FIG. 13 the course direction is indicated as vector 51 andthe warp direction is indicated by vector 53. The knitted pattern of thepresent invention has multiple patterns of diagonally shifting yarns.Such a pattern provides stretchability to the textile graft 12 and alsoprovides resiliency for the textile graft to substantially return to itsquiescent state from its stretched state.

[0055] As shown in FIG. 13, front yarns 50 f and back yarns 50 b shiftdiagonally by two needle positions in alternating closed-loops andopen-loop interlacing structures. The remaining front and back yarnsalso have alternating and repeating closed-loop and open-loopinterlacing structures, but have different needle offsets. For example,back yarn 52 b has a closed-loop, and open-loop shifted diagonally in athree-by-one needle shift, followed by a closed-loop at a one-by-oneneedle shift, followed by a three-by-one needle shift for an open-loopand then followed by a closed-loop at an one-by-one needle shift. Asused herein, open loops refer to interlacing tarns where a front or aback yarn does not cross over itself in forming the loop. Also, as usedherein, closed-loops refer to interlacing yarns where a front or a backyarn crosses over itself in forming the loop. Other patterns useful withthe practice of the present invention are illustrated in FIG. 13. All ofthe different patterns are generally referred to as Atlas ormodified-Atlas knit stitches because of their diagonally alternating andrepeating patterns.

[0056] To knit textile patterns useful with the present invention,double needle bar warp-knitting machine with multiple beams or guidebars is used to form a flat-knitted seamless tubular structure. Thethreading pattern for each guide bar is shown below in Table 1, and thearrangement of each needle for the guide bar is shown below in Table 2.TABLE 1 Guide Bar Threading Details Guide Bar y - Threaded / n - NotThreaded Settings 1 y y y y y y y y y y n n 2 n n n n n n n n n n y n 3y n n n n n n n n n n n 4 n n n n n n n n n n n y 5 y n n n n n n n n nn n 6 y y y y y y y y y y n n

[0057] TABLE 2 Guide Bar Positions Guide Bar Positions 1 4-6 / 4-4 / 4-2/ 2-2 / 2-0 / 2-2 / 2-4 / 4-4 / (repeat once) 2 2-4 / 2-2 / 2-2 / 2-0 /0-2 / 0-0 / 0-0 / 0-2 / (repeat once) 3 2-2 / 2-0 / 2-4 / 4-4 / 4-4 /4-2 / 4-2 / 2-2 / (repeat once) 4 0-0 / 0-2 / 0-2 / 2-2 / 2-2 / 2-4 /2-0 / 0-0 / (repeat once) 5 4-2 / 4-4 / 4-4 / 4-2 / 2-0 / 2-2 / 2-2 /2-4 / (repeat once) 6 2-2 / 2-0 / 2-2 / 2-4 / 4-4 / 4-6 / 4-4 / 4-2 /(repeat once)

[0058] The knitted textile graft of the present invention is desirablymade on a warp-knitting machine (not shown) using a 14 bar double needlebar Raschel knitting machine. A useful number of needles per centimeterfor warp knitting is from about 7 to about 14 (about 18 to about 36needles per inch). About 11 needles per centimeter (28 needles per inch)are particularly suitable. The textile graft is usually made from a yarnhaving count from 30 to 300 denier. Desirably, the range of yarn densityis from about 30 to about 80 denier. A particularly suitable yarn countis about 40 denier. Moreover, the yarn may be a single ply, a double plyor a multi-ply. The term “multi-ply” is used herein to indicate morethan two-ply.

[0059] Furthermore, the knitted textile graft of the present inventionhas greater than 350 stitches per square centimeter, for instance fromabout 400 to about 900 stitches per square centimeter (about 2,500 toabout 6,000 stitches per square inch), to provide compliancy of thegraft. Desirably, the present invention has from about 500 to about 700stitches per square centimeter (about 3,200 to about 4,500 stitches persquare inch). Moreover, the knitted textile graft of the presentinvention has from about 20 to about 30 courses or wales per centimeter(about 50 to about 80 courses or wales per inch) to provide compliancyof the graft. Desirably, the present invention has from about 22 toabout 27 courses or wales per centimeter (about 57 to about 67 wales orcourses per inch). The number of courses and wales may be the same ordifferent.

[0060] In one aspect of the present invention, the knitted textile graftis a knit structure of a single layer with a two-step Atlas movement.Because of the single layer construction the textile wall thickness isminimized to yield a low profile knitted textile graft. The textile wallthickness is from about 0.3 to about 0.4 millimeters. Desirably, thetextile wall thickness is from about 0.33 to about 0.36 millimeters.Furthermore, the knitted textile graft of the present invention has aburst strength from about 10 to about 17 kg/cm² (about 150 psi to about240 psi). Desirably, the knitted textile graft of the present inventionhas a burst strength from about 12 to about 14 kg/cm² (about 170 psi toabout 200 psi). The stretchability of the knitted textile graft is 50 to200 percent at a one-kilogram of load. Knitted textile grafts with astretchability of about 75 to 180 percent at one-kilogram load are alsouseful. Furthermore, knitted textile grafts with a stretchability ofabout 100 to 140 percent at one-kilogram load are also useful.

[0061] In a typical method of warp knitting the back yarn is fed fromtwo inside beams, each beam being a spool holding a plurality of ends.Outside beams may be used in conjunction with the inside beams; theoutside beams being used for feeding the front yarns. Each outside beamalso has a plurality of ends. It should be noted, however, that theinside beams may be used for feeding the front yarn and the outsidebeams used for feeding the back yarn. Regardless of which beams areused, texturized flat yarn is generally used for both the front and backyarns. The minimum number of beams used in making the textile graft ofthe present invention is 2. A greater number of beams, however, may befound useful for specific applications. Six guide beams or guide barshave been found to be particularly useful with the practice of thepresent invention.

[0062] Any type of textile product can be used as yarns for the knittedtextile graft of the present invention. Of particular usefulness informing the knitted fabric prosthesis of the present invention aresynthetic materials such as synthetic polymers. Synthetic yarns suitablefor use in the present invention include, but are not limited to,polyesters, including PET polyesters, polypropylenes, polyethylenes,polyurethanes and polytetrafluoroethylenes. The yarns may be of themonofilament, multifilament, spun type or combinations thereof. Theyarns may also be flat, twisted or textured, and may have high, low ormoderate shrinkage properties or combinations thereof

[0063] The yarns used in forming the textile grafts of the presentinvention may be flat, twisted, textured or combinations thereofFurthermore, the yarns may have high, low or moderate shrinkageproperties or combination of different shrinkage properties.Additionally, the yarn type and yarn denier can be selected to meetspecific properties desired for the prosthesis, such as porosity andflexibility. The yarn denier represents the linear density of the yarn(number of grams mass divided by 9,000 meters of length). Thus, a yarnwith a small denier would correspond to a very fine yarn whereas a yarnwith a larger denier, e.g., 1000, would correspond to a heavy yarn. Theyarns used with the present invention may have a denier from about 20 toabout 200, preferably from about 30 to about 100. Preferably, the yarnsare polyester, such as polyethylene terephthalate (PET), and morepreferably the yarns are one ply, 40 denier, 27 filament flat andtexturized polyester.

[0064] After knitting the textile graft of the present invention isoptionally cleaned or scoured in a basic solution of warm water, e.g.,about 50° C. to about 65° C. (about 120° F. to about 150° F.), anddetergent. The textile is then rinsed to remove any remaining detergent.

[0065] After the textile graft is optionally scoured, the graft iscompacted or shrunk to reduce and control, in part, the porosity of thegraft. Porosity of a knitted material is measured on the Wesolowskiscale and by the procedure of Wesolowski. In the Wesolowski test, afabric test piece is clamped flatwise and subjected to a pressure headof about 120 mm. of mercury. Readings are obtained which express thenumber of millimeters of water permeating per minute through each squarecentimeter of fabric. A zero reading represents absolute waterimpermeability and a value of about 20,000 represent approximate freeflow of fluid.

[0066] The porosity of the textile graft 12 is often from about 7,000 toabout 15,000 on the Wesolowski scale after being knitted on the doubleneedle bar Raschel knitting machine. A more desirable porosity is fromabout 30 to about 5,000 on the Wesolowski scale and textile graft iscompacted or shrunk in the wale direction to obtain the desiredporosity. A solution of an organic component, such ashexafluoroisopropanol or trichloroacetic acid, and a halogenatedaliphatic hydrocarbon, such as methylene chloride, is used to compactthe textile graft by immersing it into the solution for up to 30 minutesat temperatures from about 15° C. to about 160° C. Other compactingsolutions may suitably be used, such as those disclosed in U.S. Pat.Nos. 3,853,462 and 3,986,828, whose contents are incorporated byreference herein.

[0067] As noted above, preferably the tubular-knitted graft of thepresent invention is constructed of polyester which is capable ofshrinking during a heat-set process. For instance, such grafts aretypically flat-knitted in a tubular form. Due to the nature of theflat-knitting process, the tubular graft is generally flat in shapeafter knitting. Such grafts, however, when constructed of shrinkablepolyester yarn, can be heat set on a mandrel to form a generallycircular shape.

[0068] Such a heat-setting process is accomplished by first knitting thegraft in a seamless tubular form out of a material capable of shrinkingduring a heat-setting or similar process. The graft may be preshrunkbefore it is placed on a mandrel. Preshrinking may be achieved bysubmitting the woven graft to moderate temperatures, such as from 90° C.to about 205° C. (about 190° F. to about 400° F.). Usually the graft isplaced in a medium for the preshrinking. Such a medium can includewithout limitation hot water, a chemical fluid, such as methylenechloride, or a gas, such as air or carbon dioxide. The graft of thepresent invention, however, may suitably be made without such apreshrinking of the yarns.

[0069] After the graft is knitted or alternatively knitted andpreshrunk, the graft is placed on a mandrel, and heated in an oven at atemperature and time capable of causing the yarns of the graft to heatset to the shape and diameter of the mandrel. Preferably polyester yarnsare used, and the heat setting is accomplished at time and temperaturesappropriate for the material. For example, heat setting can beaccomplished at about 90° C. to about 225° C. (about 190° F. to about437° F.) for a period of about less than an hour. Temperatures in therange of about 130° C. to about 220° C. (about 260° F. to about 428° F.)are also useful. Desirably, temperatures from about 150° C. to about215° C. (about 300° F. to about 419° F.) are also useful. Desirably,time periods from about 5 to about 30 minutes are useful. Moredesirably, with time periods from about 10 to about 20 minutes areuseful. Other methods of heat setting known in the art may be employed.After such a heat setting process, the graft can be formed into a shapedesired for implantation, having a generally circular inner lumen.

[0070] In another aspect of the present invention stent-graft 10 furtherincludes a non-textile layer 13, as depicted in FIG. 14. The non-textilelayer is circumferentially disposed between textile graft 12 and stent14 and securably attached therebetween. One type of non-textile materialparticularly useful is polytetrafluoroethylene (PTFE). PTFE exhibitssuperior biocompatibility and low thrombogenicity, which makes itparticularly useful as vascular graft material in the repair orreplacement of blood vessels. Desirably the non-textile layer is atubular structure manufactured from expanded polytetrafluoroethylene(ePTFE). The ePTFE material has a fibrous state which is defined byinterspaced nodes interconnected by elongated fibrils. The space betweenthe node surfaces that is spanned by the fibrils is defined as theinternodal distance. When the term expanded is used to describe PTFE, itis intended to describe PTFE which has been stretched, in accordancewith techniques which increase the internodal distance and concomitantlyporosity. The stretching may be in uni-axially, bi-axially, ormulti-axially. The nodes are spaced apart by the stretched fibrils inthe direction of the expansion.

[0071] Desirably, the ePTFE material is a physically modified ePTFEtubular structure having enhanced axial elongation and radial expansionproperties of up to 600 percent by linear dimension. The physicallymodified ePTFE tubular structure is able to be elongated or expanded andthen returned to its original state without an elastic force existingtherewithin. Such a physically modified ePTFE tubular structure isadvantageously used in conjunction with wire-stent 22 of stent-graft 10.

[0072]FIG. 16 is a photomicrograph of a traditionally longitudinallyexpanded ePTFE tubular structure. The tube has been stretched in thelongitudinal direction shown by directional arrow 102, leaving the nodescircumferentially oriented in circumferential direction shown by thedirectional arrow 104. The fibrils 106 are shown as being uniformlyoriented in the longitudinal direction shown by directional arrow 102.Nodes 108 are shown and are uniformly oriented in circumferentialdirection 104.

[0073]FIG. 17 is a photomicrograph of the physically modified ePTFEtubular structure having circumferentially oriented nodes andlongitudinally traversing fibrils. Nodes 110 are shown in thephotomicrograph with a set of fibrils with first ends 112 and secondends 114 attached thereto. The fibrils with first ends 112 and secondends 114 are shown in a hingeably rotated position so that they are notsubstantially longitudinally oriented in the direction shown bydirectional arrow 102 as compared to the substantially longitudinallyoriented parallel fibril structures 106 of FIG. 16. The term “hingeablyrotated” and variants thereof refer to reorientation of previouslyuniformly oriented line segments by a change in position of one end ofeach line segment in relation to the other end of each segment, whichremains fixed; i.e., the “hinge” about which the other end rotates. Thereorientation takes place without a substantial change in dimension ofthe line segment. Additional details of the physically-modified ePTFEand methods for making the same can be found in commonly assignedapplication titled, “ePTFE Graft With Axial Elongation Properties”,filed on date herewith, attorney docket 498-256, the contents of whichare incorporated by reference herein.

[0074]FIG. 15 is a partial perspective view of an implantable medicalfabric 40, another aspect of the present invention. The medical fabric40 is a warp-knitted textile fabric having Atlas and modified-Atlaspatterns as described above. The medical fabric 40 has the features ofthe above-described textile graft 12, for instance, a high degree ofstretchability. The medical fabric 40 of the present invention is usefulin intraluminal applications, such as hernia repair.

[0075] The invention may be further understood with reference to thefollowing non-limiting examples.

EXAMPLES EXAMPLE 1 Single Layer Knit Tubular Graft With a Two-Step AtlasMovement

[0076] The following specifications are used to fabricate a solidknitted prosthesis of the present invention.

[0077] Yarn Type: Texturized polyethylene terephthalate (PET), 40denier, 27 filaments.

[0078] Number of Guide Bars: Six.

[0079] Guide Bar Threading Details: (y—Threaded/n—Not Threaded)

[0080] Guide Bar No. 1: y/y/y/y/y/y/y/y/y/y/n/n

[0081] Guide Bar No. 2: n/n/n/n/n/n/n/n/n/n/y/n

[0082] Guide Bar No. 3: y/n/n/n/n/n/n/n/n/n/n

[0083] Guide Bar No. 4: n/n/n/n/n/n/n/n/n/n/n/y

[0084] Guide Bar No. 5: y/n/n/n/n/n/n/n/n/n/n/n

[0085] Guide Bar No. 6: y/y/y/y/y/y/y/y/y/y/n/n

[0086] Guide Bar Position Details:

[0087] Guide Bar No. 1: 4-6/4-4/4-2/2-2/2-0/2-2/2-4/4-4/1 (repeat once)

[0088] Guide Bar No.2: 2-4/2-2/2-2/2-0/0-2/0-0/0-0/0-2/(repeat once)

[0089] Guide Bar No. 3: 2-2/2-0/2-4/4-4/4-4/4-2/4-2/2-2/(repeat once)

[0090] Guide Bar No. 4: 0-0/0-0/2-0/2-2/2-2/2-2/4-2/0-0/0/(repeat once)

[0091] Guide Bar No. 5: 4-2/4-4/4-4/4-2/2-0/2-2/2-2/2-4/(repeat once)

[0092] Guide Bar No. 6: 2-2/2-0/2-2/2-4/4-4/4-6/4-4/4-2/(repeat once)

[0093] Graft Processing:

[0094] Subsequent to knitting the textile graft, the material wasscoured in a basic solution of warm water (e.g., about 65° C. or about150° F.) and cleaning detergent. It was then rinsed to remove thecleaning agents. The graft was then compacted with methylene chloride atelevated temperatures, for instance about 107° C. or about 224° F., fora short period of time, for instance, three minutes.

[0095] Next, the prosthesis was heat-set on stainless steel mandrels toachieve the final desired inside diameter. Typically, the outsidediameter of the mandrel was twenty to forty percent oversized to impart,in part, a high stretch characteristic to the textile graft. Heatsetting was accomplished in a convection oven at about 212° C. (about414° F.) for about 10 minutes.

[0096] Although illustrative embodiments of the present invention havebeen described herein with reference to the accompanying drawings, it isto be understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention.

What is claimed is:
 1. An implantable tubular prosthesis capable oflongitudinal expansion from a quiescent state to an elongated statecomprising: a radially contractible and longitudinally expandabletubular stent having a quiescent diameter and quiescent length capableof longitudinal expansion to the elongated state having an elongatedlength and a contracted diameter, wherein the elongated length isgreater than the quiescent length and the contracted diameter is smallerthan the quiescent diameter, and further wherein said stent is capableof resiliently returning from the elongated state to the quiescentstate; and a tubular knitted tubular graft circumferentially disposedand securably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeters to provide compliancy in thequiescent state.
 2. The prosthesis of claim 1 wherein the elongatedlength is at least about 50 percent by length greater than the quiescentlength; and further wherein the elongated length is no more than about200 percent by length greater than the quiescent length.
 3. Theprosthesis of claim 1 wherein said graft has at least about 500 stitchesper square centimeter; and further wherein said graph has no more thanabout 700 stitches per square centimeter.
 4. The prosthesis of claim 1wherein the elongated length is at least about 100 percent by lengthgreater than the quiescent length; and further wherein the elongatedlength is no more than about 140 percent by length greater than thequiescent length.
 5. The prosthesis of claim 1 wherein said graft issubstantially fluid-tight in the quiescent state.
 6. The prosthesis ofclaim 1 wherein said knit pattern is a warp knitted pattern of yarnsforming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns comprise the interior surface and formloops in the longitudinal direction of said prosthesis, and exterioryarns comprise the exterior surface and are diagonally shifted over oneor more of the interior yarns in an alternating pattern along a width ofsaid prosthesis to engage the interior yarns, and further wherein theinterior yarn alternately interlaces the engaging exterior yarn to formopen loops where the interior yarn does not cross over itself and closedloops where the interior yarn does cross over itself.
 7. The prosthesisof claim 1 wherein said knit pattern is an Atlas or a modified Atlasknit pattern.
 8. The prosthesis of claim 1 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 9. Theprosthesis of claim 1 wherein said graft is a single layer of interlacedyarns.
 10. The prosthesis of claim 1 wherein said graft has a wallthickness of at least about 0.3 millimeters; and further wherein saidgraft has a wall thickness no more than about 0.4 millimeters.
 11. Theprosthesis of claim 1 wherein said graft is securably attached atintermediate positions along the length of said stent.
 12. Theprosthesis of claim 11 wherein said graft non-bulgingly contracts fromthe elongated state to the quiescent state to circumferentially abutsaid stent.
 13. The prosthesis of claim 1 wherein said stent has aninterior circumferential surface and further wherein said graft iscircumferentially disposed to said interior surface.
 14. The prosthesisof claim 1 wherein said stent has an exterior circumferential surfaceand further wherein said graft is circumferentially disposed to saidexterior surface.
 15. The prosthesis of claim 1 further including atubular layer of ePTFE circumferentially disposed and securably attachedto said stent.
 16. The prosthesis of claim 15 wherein said tubular layerof ePTFE is circumferentially disposed between said stent and saidgraft.
 17. The prosthesis of claim 1 wherein said stent is a wire-stent.18. The prosthesis of claim 1 wherein said yarns are selected from thegroup consisting of monofilament yarns, multifilament yearns, spun typeyarns, flat yarns, twisted yarns, textured yarns, and combinationsthereof.
 19. The prosthesis of claim 1 wherein said yarns are selectedfrom the group of materials selected from polyesters, polypropylenes,polyethylenes, polyurethanes, polytetrafluoroethylenes or combinationsthereof.
 20. The prosthesis of claim 19 wherein said polyesters includepolyethylene terephthalate polyesters.
 21. The prosthesis of claim 1wherein said yarns are polyethylene terephthalate polyester texturedyarns having a denier of at least about 30; and further wherein saidpolyethylene terephthalate polyester textured yarns have a denier of nomore than about
 100. 22. The prosthesis of claim 1 wherein said patternhas at least 20 stitches per centimeter in the longitudinal direction ofsaid prosthesis; and further wherein said pattern has no more than about30 stitches per centimeter in the longitudinal direction of saidprosthesis.
 23. The prosthesis of claim 1 wherein said pattern has atleast about 20 stitches per centimeter along the width of saidprosthesis; and further wherein said pattern has no more than about 30stitches per centimeter along the width of said prosthesis.
 24. Animplantable tubular prosthesis capable of radial expansion from aquiescent state to a radially expanded state comprising: a radiallyexpandable and longitudinally contractible tubular stent having aquiescent diameter and quiescent length capable of radial expansion tothe radially expanded state having an expanded diameter and a contractedlength, wherein the expanded diameter is greater than the quiescentdiameter and the contracted length is smaller than the quiescent length;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient radial expansion and resilient longitudinalcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeter to provide compliancy in thequiescent state.
 25. The prosthesis of claim 24 wherein the quiescentlength is at least about 50 percent by length greater than thecontracted length; and further wherein the quiescent length is no morethan about 200 percent by greater than the contracted length.
 26. Theprosthesis of claim 24 wherein said knit pattern is a warp knittedpattern of yarns forming a textile layer having an interior surface andan exterior surface, wherein interior yarns predominate the interiorsurface and form loops in the longitudinal direction of said prosthesis,and exterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yarn alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yarn does cross overitself.
 27. The prosthesis of claim 24 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 28. Theprosthesis of claim 24 wherein said graft is a single layer ofinterlaced yarns.
 29. The prosthesis of claim 24 wherein said graft hasa wall thickness of at least 0.3 millimeters, and further wherein saidgraft has a wall thickness no more than 0.4 millimeters.
 30. Theprosthesis of claim 24 further including a tubular layer of e-PTFEcircumferentially disposed and securably attached to said stent.
 31. Theprosthesis of claim 24 wherein said stent is a slotted-stent.
 32. Theprosthesis of claim 24 wherein said yarns are polyethylene terephthalatepolyester textured yarns having a denier of at least about 30; andfurther wherein said polyethylene terephthalate polyester textured yarnshave a denier no more than about
 80. 33. The prosthesis of claim 24wherein said graft is longitudinally stretched to circumferentiallyencompass said stent in the quiescent state of said prosthesis.
 34. Animplantable tubular prosthesis capable of longitudinal expansion from aquiescent state to an elongated state comprising: a radiallycontractible and longitudinally expandable tubular stent having aquiescent diameter and quiescent length capable of longitudinalexpansion to the elongated state having an elongated length and acontracted diameter, wherein the elongated length is greater than thequiescent length and the contracted diameter is smaller than thequiescent diameter, and further wherein said stent is capable ofresiliently returning from the elongated state to the quiescent state;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeter to provide compliancy in thequiescent state; wherein said knit pattern is a warp knitted pattern ofyarns forming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns predominate the interior surface andform loops in the longitudinal direction of said prosthesis, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yarn alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yarn does cross overitself.
 35. The prosthesis of claim 34 wherein the elongated length isat least about 50 percent by length greater than the quiescent length;and further wherein the elongated length is no more than about 200percent by length greater than the quiescent length.
 36. The prosthesisof claim 34 wherein said knit pattern comprising a interior and exterioryarns interlaced from single stitches, said single stitches beingdeposed in a plurality of stitch repeating patterns, wherein a firststitch has a repeating pattern traversing diagonally by two or moreneedle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 37. The prosthesis of claim 34 whereinsaid graft has a wall thickness of at least about 0.3 millimeters; andfurther wherein said graft has a wale thickness of no more than about0.4 millimeters.
 38. The prosthesis of claim 36 further including atubular layer of e-PTFE circumferentially disposed and securablyattached to said stent.
 39. The prosthesis of claim 34 wherein saidstent is a wire-stent.
 40. The prosthesis of claim 34 wherein said yarnsare polyethylene terephthalate polyester textured yarns having a denierfrom about 30 to about
 100. 41. An implantable tubular prosthesiscapable of longitudinal expansion from a quiescent state to an elongatedstate comprising: a radially contractible and longitudinally expandabletubular stent having a quiescent diameter and quiescent length capableof longitudinal expansion to the elongated state having an elongatedlength and a contracted diameter, wherein the elongated length isgreater than the quiescent length and the contracted diameter is smallerthan the quiescent diameter, and further wherein said stent is capableof resiliently returning from the elongated state to the quiescentstate; and a tubular knitted tubular graft circumferentially disposedand securably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having greater thanabout 350 stitches per square centimeter to provide compliancy in thequiescent state; wherein the elongated length is at least 50 percent bylength greater than the quiescent length; and further wherein theelongated length is no more than about 200 percent by length greaterthan the quiescent length.
 42. The prosthesis of claim 41 wherein saidknit pattern is a warp knitted pattern of yarns forming a textile layerhaving an interior surface and an exterior surface, wherein interioryarns predominate the interior surface and form loops in thelongitudinal direction of said prosthesis, and exterior yarnspredominate the exterior surface and are diagonally shifted over one ormore of the interior yarns in an alternating pattern along a width ofsaid prosthesis to engage the interior yarns, and further wherein theinterior yarn alternately interlaces the engaging exterior yarn to formopen loops where the interior yarn does not cross over itself and closedloops where the interior yarn does cross over itself.
 43. The prosthesisof claim 41 wherein said knit pattern comprising a interior and exterioryarns interlaced from single stitches, said single stitches beingdeposed in a plurality of stitch repeating patterns, wherein a firststitch has a repeating pattern traversing diagonally by two or moreneedle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 44. The prosthesis of claim 41 furtherincluding a tubular layer of ePTFE circumferentially disposed andsecurably attached to said stent.
 45. The prosthesis of claim 41 whereinsaid stent is a wire-stent.
 46. The prosthesis of claim 41 wherein saidyarns are polyethylene terephthalate polyester textured yarns having adenier of at least 30; and further wherein said polyethyleneterephthalate polyester textured yarns have a denier of no more thanabout
 100. 47. An implantable tubular prosthesis capable of longitudinalexpansion from a quiescent state to an elongated state comprising: aradially contractible and longitudinally expandable tubular stent havinga quiescent diameter and quiescent length capable of longitudinalexpansion to the elongated state having an elongated length and acontracted diameter, wherein the elongated length is greater than thequiescent length and the contracted diameter is smaller than thequiescent diameter, and further wherein said stent is capable ofresiliently returning from the elongated state to the quiescent state;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having greater thanabout 350 stitches per square centimeter to provide compliancy in thequiescent state; wherein said interlaced stitches of said graft form agraft wall and further wherein said graft wall has a wall thickness ofat least 0.3 millimeters; and further wherein said graft wall has a wallthickness of no more than about 0.4 millimeters.
 48. The prosthesis ofclaim 47 wherein said knit pattern is a warp knitted pattern of yarnsforming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns predominate the interior surface andform loops in the longitudinal direction of said prosthesis, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yarn alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yarn does cross overitself.
 49. The prosthesis of claim 47 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 50. Theprosthesis of claim 47 further including a tubular layer of ePTFEcircumferentially disposed and securably attached to said stent.
 51. Theprosthesis of claim 47 wherein said stent is a wire-stent.
 52. Theprosthesis of claim 47 wherein said yarns are polyethylene terephthalatepolyester textured yarns having a denier of at least about 30; andfurther wherein said polyethylene terephthalate polyester textured yarnshave a denier of no more than about
 80. 53. An implantable tubular graftcomprising: a tubular knitted tubular graft having a pattern of yarnsinterlaced into stitches in a knit pattern capable of resilientlongitudinal elongation and resilient radial contraction of said graftfrom a quiescent state to the elongated state and having at least about400 to 900 stitches per square centimeter and further having no morethan about 900 stitches per square centimeter to provide compliancy inthe quiescent state; wherein said knit pattern is a warp knitted patternof yarns forming a textile layer having an interior surface and anexterior surface, wherein interior yarns predominate the interiorsurface and form loops in the longitudinal direction of said graft, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said graft to engage the interior yarns, and furtherwherein the interior yarn alternately interlaces the engaging exterioryarn to form open loops where the interior yarn does not cross overitself and closed loops where the interior yarn does cross over itself.54. The graft of claim 53 wherein said knit pattern comprising ainterior and exterior yarns interlaced from single stitches, said singlestitches being deposed in a plurality of stitch repeating patterns,wherein a first stitch has a repeating pattern traversing diagonally bytwo or more needle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 55. The graft of claim 53 wherein saidyarns are polyethylene terephthalate polyester textured yarns having adenier of at least 30; and further wherein said polyethyleneterephthalate polyester textured yarns having a denier of no more than80.
 56. A knitted medical fabric comprising: a knitted structure havinga pattern of yarns interlaced into stitches in a knit pattern capable ofresilient longitudinal expansion from a quiescent state and having atleast about 400 stitches per square centimeter and further having nomore than about 900 stitches per square centimeter to provide compliancyfor the structure; wherein said knit pattern is a warp knitted patternof yarns forming a textile layer having a first surface and a secondopposed surface, wherein a first yarn predominates the first surface andforms loops in the longitudinal direction of said fabric, and a secondyarn predominates the second surface and is diagonally shifted over oneor more of the first yarns in an alternating pattern along a width ofsaid fabric to engage the first yarn, and further wherein the secondyarn alternately interlaces the engaging first yarn to form an open loopwhere the second yarn does not cross over itself and a closed loop wherethe second yarn does cross over itself.
 57. The medical fabric of claim56 wherein said first and second yarns are formed from single stitches,said single stitches being deposed in a plurality of stitch repeatingpatterns, wherein a first stitch has a repeating pattern traversingdiagonally by two or more needle positions and a second stitch has arepeating pattern alternatively traversing diagonally by three or moreneedle positions and then by one needle position.
 58. The medical fabricof claim 56 wherein said yarns are polyethylene terephthalate polyestertextured yarns having a denier of at least about 30; and further whereinsaid polyethylene terephthalate polyester textured yarns having a denierof no more than about
 100. 59. A process for making an implantabletubular prosthesis capable of longitudinal elongation or contractionfrom a quiescent state to a second state comprising: selecting at leasttwo yarns; selecting a knit pattern of said yarns capable of forming atubular fabric layer and further capable of the resilient longitudinalelongation or contraction, wherein said loose knit pattern is a warpknitted pattern of yarns forming a textile layer having an interiorsurface and an exterior surface, wherein an interior yarn predominatesthe interior surface and forms loops in the longitudinal direction ofsaid prosthesis, and an exterior yarn predominates the exterior surfaceand is diagonally shifted over one or more of the interior yarns in analternating pattern along a width of said prosthesis to engage theinterior yarns, and further wherein the interior yarn alternatelyinterlaces the engaging exterior yarn to form open loops where theinterior yarn does not cross over itself and closed loops where theinterior yarn does cross over itself; and knitting said knit patternwith at least 400 stitches per square centimeter but with no more thanabout 900 stitches per square centimeter to provide compliancy for theknit pattern.
 60. The process of claim 59 further comprising heatsetting said tubular fabric layer to form a tubular graft.
 61. Theprocess of claim 59 further comprising selecting a tubular stent capableof resilient longitudinal elongation or contraction and securablyattaching said tubular fabric layer to said stent at intermediatepositions along the length of said stent.
 62. The process of claim 59wherein selecting said yarns includes selecting from the groupconsisting of monofilament yarns, multifilament yearns, spun type yarns,flat yarns, twisted yarns, textured yarns, and combinations thereof. 63.The process of claim 59 wherein selecting said yarns includes selectingfrom the group of materials selected from polyesters, polypropylenes,polyethylenes, polyurethanes, polytetrafluoroethylenes or combinationsthereof.
 64. The process of claim 63 wherein said polyesters areselected from polyethylene terephthalate polyesters.
 65. The process ofclaim 59 wherein selecting said yarns includes selecting polyethyleneterephthalate polyester textured yarns having a denier of at least about30, and further selecting Polyethylene terephthalate polyester texturedyarns having a denier of no more than about 80.